Police are warning female college students in Columbia to take extra precautions after a series of early-morning break-ins and sexual assaults that may be connected to a similar spate of attacks last year.

Investigators suspect that six incidents between May 1 and May 9 may be related, said Columbia police spokeswoman Latisha Stroer.

In each instance, a college-age woman reporting finding a male who broke into her apartment or attempted to enter between 3:30 a.m. and 7:15 a.m. at The Domain apartment complex on East Stadium Boulevard, and at residences in the 4100 block of Lenoir Street and the 2200 block of Grindstone Parkway.

The crimes included one sexual assault and a second attempted sex assault by an assailant with a knife.

In three instances, the apartments’ front doors were left unlocked.

A police news release notes that the crimes are similar to a series of break-ins and assaults in downtown Columbia and the East Campus neighborhood between late June and early November of 2013. Each of those break-ins involved unlocked front doors and occurred between 12:30 a.m. and 6 a.m.

The intruder is described as a white male in his 30’s, between 6 feet and 6 feet 2 inches tall, who may wear glasses and has an athletic build.